Discussion

The coldest air mass since last spring will plunge from Canada during the middle of next week into the northern Rockies, Plains and Midwest. Temperatures are likely to drop to below freezing in many locations from the northern Rockies across the northern Plains and there can even be some unusual very early snow in spots. This cold air outbreak will spread eastward and southward so that the chilliest air of the season so far reaches the I-95 corridor at the end of next week. This end-of-the-week cool shot for us will follow close behind an early week cooler-than-normal air mass that arrives here on Sunday.

The progression of this impressive early season Canadian blast of cold air can be followed on these temperature anomaly maps for next Wednesday, Thursday and Friday using NOAA’s GFS computer forecast model [maps provided by Dr. Ryan Maue at Weather Bell Analytics, weatherbell.com]. On Wednesday, the “blues and greens” on the map are seen in areas with below-normal temperatures as the Canadian plunge is working its way through the northern Rockies and northern Plains. Also, on Wednesday below normal temperatures can be seen across much of the Northeast US from the initial cool-down that begins here on Sunday. By Thursday, the Canadian cold shot plunges southward into the southern Plains while the Mid-Atlantic region experiences a brief period of above-normal temperatures ahead of the strong cool front. By Friday, the Canadian cold shot spreads all the way to the east coast and nearly the entire eastern 2/3rds of the nation is cooler-than-normal. High temperatures here at the end of next week and weekend are likely to be well below normal for mid-September. Some areas in the middle of the country late next week could experience temperatures 30 degrees or more below normal (“purples”).